Exposure of molecules to intense magnetic fields will induce signals (e.g., magnetic circular dichroism, magnetic linear dichroism, magnetic optical rotatory dispersion, and the like) which may augment the information gained by their spectrometric analysis. The problem lies in providing a sample holder with means of generating a magnetic field of sufficient intensity to induce measurable signals in a sample, while simultaneously minimizing its size, weight and expense.
A magnetic circular dichroism (MCD) signal is the differential absorption of left and right circularly polarized light induced in a molecular sample by an externally applied, intense magnetic field. MCD signal can augment the information provided by the measurement of absorption of a sample using ordinary light. Many biologically important molecules exhibit particularly strong MCD signals which can be detected even when present in complex mixtures. MCD measurements require the magnetic field be oriented parallel (or anti-parallel) to the direction of the measurement light beam (or beams).
Magnetic fields oriented perpendicularly to the direction of the measurement beam may produce a magnetic linear dichroism (MLD) signal by partially aligning or orienting large macromolecules and macromolecular arrays. The MLD signal may be used to study biomembranes, phospholipid membranes and other molecular constructs.
Information relevant to attempts to provide a magnetic field capable of inducing magnetic signals in molecular samples can be found in U.S. Pat. No. 3,442,592 to Grosjean; U.S. Pat. No. 3,740,151 to Chaney et al.; U.S. Pat. No. 3,801,204 to Jennings et al.; U.S. Pat. No. 4,725,140 to Musha; U.S. Pat. No. 4,818,881 to Tanton et al.; U.S. Pat. No. 5,838,444 to Jo; U.S. Pat. No. 5,706,087 to Thompson et al.; U.S. Pat. No. 6,046,804 to Kawamura et al.; and, U.S. Pat. No. 6,573,817 to Gottschalk. However, each one of these references suffers from one or more disadvantages discussed as follows.
The most commonly employed types of magnets used to generate magnetic fields are electromagnets which produce up to about 1.5 T (15,000 Gauss). Electromagnets are large and heavy preventing their easy manual manipulation by a user. They also require a large power supply and water-cooling.
Because the magnetic flux must be parallel to the measurement light beam(s) (for measuring MCD or magnetic optical rotatory dispersion (MORD)), long drillings (i.e., up to 50 cm or more) must be made through the pole pieces of the electromagnet to admit the measurement light beam(s), which beam or beams must be painstakingly aligned. The resulting drillings are minimal in diameter and result in a narrow light path which is very difficult to align properly with a single light beam, and generally precludes the use of more than one light beam. These magnets are cumbersome, expensive and difficult to install in a CD, or other type of, spectrometer. Often, the CD instrument itself must be altered to reduce the effects of the stray magnetic signals which are always produced by electromagnets.
Superconducting magnets are also available. However, though they can produce magnetic fields up to 10.0 T (100,000 Gauss), they are large, expensive and require large supplies of cryogenic gases. Their use generally requires specialized laboratories and specially trained personnel to operate them.
A third type of magnet is a permanent magnet which has advantages over the prior two in not requiring a power supply or the use of specialized facilities and personnel. However, the most powerful permanent magnets available today, produce a magnetic field strength of only about 0.7 T (7,000 Gauss) or less, making them generally inadequate to the task of inducing a significant magnetic signal in a molecular sample. The signal induced by a magnetic field in a sample is directly proportional to the field strength of the magnet. Therefore, the field strength should be as high as possible, and should generally exceed 0.7 T (7,000 Gauss) in strength. Further, these other magnets are larger and heavier and therefore difficult to manipulate.
For the foregoing reasons, there is a need for a small manually manipulatable sample holder that enables simultaneous exposure of a molecular sample to one or more beams of light and to an intense magnetic field sufficient to induce a signal in the molecular sample.